1. Field of the Invention
The present invention relates to the linking of chains generally, and more specifically to a master link for chains used with chainwheel operators.
2. Background
Chainwheel operators are known in the art. FIG. 1 depicts a schematic view of such an operator. A chainwheel 20 is attached to the handwheel of a valve, and can be accordingly likewise rotated as depicted by arrow A. A guide member 25 attaches in pivoting, hanging fashion from the center of the chainwheel, and provides two arms with chain guides at the end thereof. The chain 30 passes through the chainguides of the guide member 25 and around the chainwheel. Pulling on the chainwheel turns the chainwheel 20, and therefore the valve hand wheel to which it is attached.
Replacing the chains on a chainwheel can be cumbersome and time consuming. Usually, this will entail crimping or wrapping the end of an open link about the loop of an opposite end link using vises and locking pliers. This process cannot be easily accomplished in the field. Because of the mechanical deformation of the adjoining links where the chain ends are joined, the joint becomes quite literally the weakest link in the chain.
At least one master link has been proposed for chainwheel chains in U.S. Pat. No. 5,628,178. FIG. 2 depicts the '128 master link 40 attaching opposite ends of chain 30 riding in the channel of the chainwheel 20. FIG. 3 depicts in exploded view the prior art master link 40. A shackle body 42 is configured to receive a pressing member 44 and a bolt 46 which threadedly engages threaded bore 47. The shackle member extends to form two extensions 48 and 50 which terminate in loops. Pin 52 passes through bore 54 and thereafter threadedly engages threaded bore 56. When attached to chain ends as depicted in FIG. 2, pin 52 engages one end of the chain, and the bent tab 58 of the pressing member 44 engages the other against the shackle body 42.
The prior art master link, however, is expensive to manufacture. The design calls for a two-piece body comprising a shackle body and a press member. Further, the prior art master link is designed to be easily removable from the chain, thus the design includes expensive parts and requires assembly tolerances that may in practice not be required for most uses. However, oftentimes a master link does not need to be removed after it is attached. Further, the press member tab 58, because of its bent design, concentrates stresses at the bend, which could lead to breakage. To avoid breakage, more expensive materials are required for heavy-duty performance. Further, the very removable nature of the pressing member bolt 46 of the '128 master link as well as the pin 52 may lead to loosening and eventual disassociation of the pin 52 and bolt 46 from the shackle, leading to the separation of the chain ends. Such separation could lead to injury of the operator.